Opposition to the Obama administration's proposal to ban a popular bullet is gaining steam in the House of Representatives, where more than half of the lawmakers have signed a letter opposing the move.

The Bureau of Alcohol, Tobacco, Firearms and Explosives says it wants to ban popular .223 M855 “green tip” ammunition because the bullets can pierce bulletproof vests used by law enforcement. Although the ATF previously approved it in 1986, the agency now says that because handguns have now been designed that can also fire the bullets, police officers are now more likely to encounter them.Some 239 members of the House have now put their names to the letter opposing the ban, which they say would interfere with Americans’ Constitutional rights.

“This attack on the Second Amendment is wrong and should be overturned,” Rep. Bob Goodlatte, (R-Va.), who started the petition, said in a statement to FoxNews.com. "A clear, sizeable majority of the House agree,” he noted.

White House Press Secretary Josh Earnest backed up the agency’s proposal at a press conference on Monday.

“This attack on the Second Amendment is wrong and should be overturned.”

- Rep. Bob Goodlatte, R-Va.

“We are looking at additional ways to protect our brave men and women in law enforcement… This seems to be an area where everyone should agree that if there are armor-piercing bullets available that can fit into easily concealed weapons, that it puts our law enforcement at considerably more risk,” Earnest said.

But gun-rights groups such as the National Rifle Association note that almost all rifle bullets can pierce armor, and say that this is just an excuse for limiting civilian gun use.

“The claim that this is done out of a concern for law enforcement safety is a lie. The director of the Fraternal Order of Police has said this is not an issue of concern. And according to the FBI, not one single law enforcement officer has been killed with M855 ammunition fired from a handgun," Chris Cox, executive director of the NRA Institute for Legislative Action, told FoxNews.com.

Some law enforcement groups reached by FoxNews.com also say that they no need for the regulation.

“The notion that all of a sudden a new pistol requires banning what had long been perfectly legal ammunition doesn’t seem to make a lot of sense to many officers,” William Johnson, executive director of the National Association of Police Organizations, told FoxNews.com.

NAPO represents over 1,000 police units and associations and 241,000 law enforcement officers around the country.

But some law enforcement experts support the ban.

“I am definitely for the banning of these rounds… officers worry about them all the time,” former NYPD detective Harry Houck told FoxNews.com, though he added that a ban might not actually keep criminals from getting the ammunition.

Gun control groups support the ban.

"We understand why law enforcement has always been concerned about the threat of armor-piercing bullets," Dan Gross, president of the Brady Campaign to Prevent Gun Violence, told FoxNews.com.

Lawmakers warn that the regulation – especially as it follows on the heels of attempts to restrict lead bullets -- will “result in drastically reduced options for lawful ammunition users.” Already, the ammunition has been cleared from many store shelves by gun owners looking to stock up in anticipation of the ban. The proposed regulation would not prohibit owning the bullets, but it would stop anyone from manufacturing or importing them.

Gun-rights groups also worry that the ban – if allowed to stand – won’t stop with this type of bullet.

“Almost any hunting rifle bullet will go through body armor, so you could prohibit almost any rifle bullet with this. This is the administration redefining the law on its own,” Alan Gottlieb, of the Second Amendment Foundation, told FoxNews.com.

The lawmakers also dispute the ATF’s legal authority to ban the bullets, saying that the proposed ban “does not comport with the letter or spirit of the law.”

The law, which was passed in 1986, gives the agency authority to ban bullets that are “constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper or depleted uranium.”

However, the lawmakers say that the core of these bullets “contains a substantial amount of lead, raising questions about its classification as ‘armor piercing’ in the first place.”

The House members also allege that the ATF violated government transparency requirements.

“The Administrative Procedures Act… requires that ‘general notice of proposed rulemaking shall be published in the Federal Register…’ To date, [the proposed ban] has not been published in the Federal Register.”

The ATF has announced that it is currently taking public comments on the regulation until March 16, when it will prepare to issue a final regulation. Comments can be sent to APAComments@atf.gov.

An ATF spokesman emphasized that no final decision has been made yet.

“No final determinations have been made and we won’t make any determinations until we’ve reviewed the comments submitted by industry, law enforcement and the public at large,” ATF spokesman Corey Ray told FoxNews.com.

“The framework is… intended to protect law enforcement while respecting the interests of sportsmen and the industry,” he also noted.